Consensus refers both to a state of common feeling or agreement in a group and to a decision rule by which a group or society determines legitimate political authority and coordinates political action. The term derives from the Latin consens, which is closely related to consent, and was first used in modern times to describe the relationship between different parts of a system in working toward the purpose of the whole. Characteristic of many nineteenth-century writers, Emile Durkheim posits the analogy of a "spontaneous consensus of parts" in the body social as a necessary condition for the preservation of order in increasingly differentiated societies (1984, p. 297). Contemporary theories of communitarianism, civic culture, and liberal pluralism follow Durkheim, to different degrees, in staking democratic order on a value consensus embedded in social norms, practices, and institutions.
Theorists of participatory and deliberative democracy often abandon the search for an empirical consensus underlying social order and instead hold consensus as a normative ideal of political decision making amid human conditions of difference and conflict. For Jean-Jacques Rousseau, legitimate political authority rests not on the consent of the majority—the domination of a part of society over the whole—but on a consensus that accounts for the interests of all members of society. Consensus thus seeks to preserve individual freedom and political equality. Indebted to Immanuel Kant’s (1724-1804) theory of common sense, Jurgen Habermas (1990) locates the ideal of consensus in the fundamental practice of communication, which presupposes the possibility of shared understanding between speakers. The expectation of rational consensus inherent in speech establishes certain norms for political deliberation, most notably reason, inclusion, participation, and publicity. On many accounts, consensual politics requires both constitutionally protected public spaces and institutionalized procedures that incorporate the previous norms into decision-making processes.
Critics of consensualism worry that the ideal of consensus carries normalizing and repressive effects on groups and societies. Theorists of agonistic democracy, such as Iris Marion Young (2000) and William E. Connolly (1991), contend that commitment to a strong rational consensus privileges certain modes of expression and participation to the exclusion of others and often brackets difficult issues from public discussion altogether. Thus, consensual ideals of political engagement and outcome effectively silence some points of view. While agonistic democracy affirms the possibility of agreement on particular issues in particular circumstances, it recognizes the contingencies and exclusions that constitute any strong value consensus and emphasizes a care for difference and struggle as central elements of politics.
In practice, consensual politics have long embodied the ideals and tensions of these competing theoretical strains. While consensus was the aim, if not always the abiding practice, in the political assemblies of ancient Athens, classical writers from Thucydides (c. 460-c. 400 BCE) to Aristotle cautioned against the dangers of popular rhetoric in fomenting collective tyranny. The Iroquois Confederacy explicitly protected dissenting views during consensual processes by establishing mechanisms for veto power and for the revisiting of contentious issues. The Religious Society of Friends and the peace and environmental movements of the late twentieth century are examples of groups that use consensus decision-making practices.